The present invention relates to a power supply distribution system; and more particularly to a pulsed voltage supply for a plurality of parallel connected modules of a power amplifier.
Solid-state power amplifiers for radar applications, for example, require a high degree of pulse-to-pulse phase and amplitude stability. The principal limitation on this stability is the quality of the power supply voltage at the RF amplifier transistors that are rendered conductive to constitute a pulsed load of the appropriate frequency. Both the phase and output amplitude of a class B or C power amplifier change with variations in the voltages of these RF transistors. The required RF stability, therefore, is directly dependent upon the stability of the supply voltage; and such required voltage stability for such applications, for example, may be in the several millivolt region for high performance radar systems.
Heretofore, and referring to FIG. 1, a coarse DC voltage supply referred to at 10 may be derived by a rectifier bridge or inverter power supply, for example. A DC precision regulator 11 which is utilized to remove inverter ripple and other voltage perturbations, includes a power supply transistor 12 having its collector and emitter portions connected in series in output line 13 of the power supply 10. The precision regulator conventionally includes a voltage reference source 14 connected to the base portion of the transistor 12 to cause the transistor 12 to conduct to charge a capacitor bank 15 that is connected across the output 13 and an output 16 of the regulator 11 to provide energy storage for each of a plurality of RF amplifier modules 17 and 18. The individual modules are connected in parallel to the outputs 13 and 16 of the precision regulator 11 downstream of the capacitor 15. Each of the modules 17 and 18 may include one or more inductors such as 21 and 22 connected in series with the emitter and collector terminals of RF transistors 23 and 24, respectively. The series connected inductors and their associated RF transistors are connected across suitable conductors 25 and 26 in each respective modules 17 and 18 which are connected to the capacitor to the output leads of the regulator 11. The pulsed output may be obtained on lines 27 and 28 through parallel connected secondary inductive windings 29 and 30. A conventional amplifier 31 having an RF input is connected to the base portions of each of the transistors to drive the transistors at the appropriate frequency. A capacitor 43 which is 1 to 2% the size of the bank 15 may be connected across leads 25 and 26 of its respective module to increase the rise time of the pulses.
To summarize the operation of the prior art arrangement of FIG. 1, reference is made to the wave forms of FIG. 2. A wave form referred to as 32 illustrates the voltage at the output of the DC supply 10 at point A as shown in FIG. 1 which includes the ripple connected with such voltage and the drooping effects at 33 and 34 caused by the regulation of the load in the plurality of modules 17 and 18. A typical voltage wave form 35 occurs at the output of the regulator 11 at point B shows the ripple removed, but a slight droop in such voltage value at 36 and 37 which occurs in charging the capacitor bank 15. A wave form 38 at 39 and 40 illustrates the general nature of the current at points A and B of FIG. 1 in response to the drawing of current by the modules 18 and 17 upstream of the capacitor bank 15. Wave forms 41 and 42 represent the peak current for the duration of each of the pulses downstream of the capacitor bank 15. Each of the plurality of solid-state power modules draw high current pulses out of the common energy storage bank 15 at the RF pulse width and repetition rate to which is supplied a relatively constant current from the regulator 11. For radar applications, the pulse duty cycles may typically range from 1% to 10%. Thus, the peak currents from the capacitor bank 15 may be ten to one hundred times greater than the average current from the precision regulator 11 which recharges it. The capacitor bank 15 is required to store many times the individual pulse energy in order to minimize voltage droop during each pulse, which in turn, produces amplitude and phase droop in each of the RF pulses. In addition, the capacitor bank 15 must be precisely recharged before each pulse in order to maintain identity between successive pulses. The recharging problem may be particularly severe for applications where the pulse repetition rate is staggered. Exponential charging or lead ringing produces different recharge voltages for different interpulse periods.
Therefore, it is desirable to provide a power system for a plurality of parallel connected modules that reduces the energy storage requirements, yet improves the stability of the amplifier, and simplifies the power distribution.